1947 Mark 4, running gear

Have a 1947, Mark 4 1.5ltr, can anyone tell me the running temperature, current internal thermosat runs at 80. Which I believe is quite high, recently replaced head gasket and exhaust gaskets. Can anyone help with the left hand side internal light cover for this model. I am also concerned about the amount of travel through the worm gear to the steering wheel, no-one here seems to understand lapped-in having a company try three times.

Hi Stephen,

Your 80 degrees is ok. The covers on the interior lights are just held in place by the little spring clip below. Prise it down to extract the cover.

In my experience the largest single cause of play in the steering box is between the peg and the hole in the nut. You can gain some benefit by turning the peg through 90 degrees. It is a taper fit in the rocker arm and it has been peened over at the top.


Hi Peter,
Thanks for technical advice, realise spring clip, but looking for light cover ( not how to remove and replace).

I think MK VII have a similar cover, MKV too for all I know.
The steering box will wear where ever it can, because that’s was Messrs Burman &Douglas designed it to do.

The drop shaft can wear as will the bush but at least post war cars have tapered splines so you can grind the bottom section of the shaft true and make a new bush to match.
The big bronze nut usually wears and ideally a new NOS one is gold. If having a new one made it should be remebered the thread can not just be turned ACMEThread but the last cut must be broached with a tap,
The male thread can also wear but you are probably stuck with that , it usually wears more in the centre
Likewise the bore of the steering box can wear,
On 6 cylindermodels we had a company whose day job was grinding newsprint rollers bore the housing out the minimum to get it true, then have new bronze nuts made with the OD oversize about +.010” is about as much as they could do
Holman Eng in UK does the 6 cylinder nuts you would have to ask them about the smaller 1 1/2 litre size

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To help you in your search:
Here is a light in my '38 SS saloon, also used in Mark V DHC.

Here is a light in XK120 FHC, also Mark 1 saloon. Mark V saloon is similar but a bit longer.

Not a fan, I see…:grimacing:

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Hi Stephen.
If the same design as my 2 1/2 there are three main places of wear.

  1. The drop arm ball into the socket of the nut.
  2. The nut to worm
  3. The worm to housing.
    (also drop arm bearing if is really bad)
    I clamped each part in turn from moving and I could see the wear of each of the component when I moved the steering wheel.
    I had a new worm and nut supplied by Holman Engineering in the UK for my 2 1/2.
    This took out 95% of the play in the box.
    They mention the 1 1/2 in their website below.
    They can even make them in oversize if the wear in the housing is too great.
    Regards, Graham

Peter and I are of the opinion that the previous Marles Weller box was better. A bit heavier in the steering[ depending] but basically no free play when in good condition.
BTW I just noticed the flag next to your name
It’s too small for these ageing eyes to identify. Is it Republic of China [ peoples for the use of] ?

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Good eye: drives rightwingers NUTS!!!






I’ll try Holman – engineering. Thanks.



Can anyone confirm the identity of this steering box, I bought it awhile ago with some SS parts that I needed? Supposedly it is a SS 1.5 litre box, are they the same as a 1.5 litre Mk 1V box? The overall length to the tip of the inner column is 1180mm.

Cheers Peter

Not an absolute confirmation, but the '38-46 parts catalogue says all 1.5 L '38-46 used the same steering unit, and it has 4 bolts in the top cover.
The 2-1/2 L and 3-1/2 L steering units have 6 bolts in the top cover.

The mounting bolt holes. From memory I tought they were the same [ basically on the 4 and 6 cylinder steel bodied carrs. These are different
But Similar boxes went in a number of cars
It may also be from a 36/7 1 1/2 litre which may have had different mounting blts as it was quite different chassis.
However the nut on the end f the drop shaft means it has tapered splines which were pre war . and make it easier to true the shaft up.
One might try counting turns lock to lock as they were variations [ 2 1/2 for SS 6 cylinder cars/ 3 1/2 for MK IVs.
Essentially the important things is , how good is the worm and the nut?

I don’t personally think the ball on the pin is a major source of free play usually. and getting a new/ remade one back in could be fraught. When the factory peaned them over they must have been set up to do it. One certainly would want to weld it in… I did try making one and peaning it in but could never get it tight enough to feel happy about it.
And there is a big risk factor in not getting steering item right.

The nice thing about this particular cause is that you easily see the drop arm moving without the nut moving. So, as a cause of wear it doesn’t need to be one of conjecture.


Just make sure the sector shaft is kept pushed right down in the box Peter, when you try the slackness test with the wheel. With the steering box cover off, the sector shaft can ride up easily (I find it always wants to ride up) and it simulates a wear gap. The ball end and the mating sleeve, which is shrink fitted in the nut, are of a high grade and/or hardened steel with a very slow wear rate. The thread in the bronze nut is the first sacrificial wear part because of its relative softness. On all the boxes I’ve worked on, it has always been the thread wear in the nut as being by far the major culprit. The second point of wear failure is any bushes for the sector shaft, followed by the ball end and mating liner in the nut. Just some thoughts from my limited experience.

For sure, you need good bushes for the sector shaft and a good nut but it’s not difficult to measure the ball end and I think most people with slack steering will find the ball measures smaller sideways than it does when measured at right angles. As to the rocker shaft riding up, this is likely to take you to a point of lesser wear in the mating sleeve as the sleeve has parallel sides.


And with 2 people and the cover off the box, and the oil mopped up, the person under the bonnet can put large screwdrivers, one each side of the nut and wedged against the box housing while the one at the steering wheel rocks it each way. This will hold the bronze nut relatively firm and one can see the wear between worm and nut. Done in the straight ahead position because that’s where most of the wear will be. Unless the car spent its career racing a Indianopolis where due to only ever turning left it will have all the wear at one end.

OK Paul, . How do you change your flag logo? . And is there one for Kurdistan? If not RKN will do.

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Hi Ed,

Thanks again.